The hypothesis being tested that normal pregnancy is characterized by increased endothelial-dependent vasodilation and decreased vascular smooth muscle vasoconstriction and that these changes are reversed early in pregnancies complicated by preeclampsia and/or maternal hypoxia. Studies of forearm vasodilation and vasoconstriction, endothelial dysfunction, cardiac output and systemic vascular resistance are underway in normal and preeclamptic pregnant women. Results to date indicate progressive reduction in vasoconstrictor response to angiotension II infusion and increased endothelium-independent vasodilation in normal pregnancy. Preeclamptic women appear to be characterized by augmented vasoconstrictor but unaltered vasodilator responsiveness.